1. Field of the Invention
The present invention relates to a temperature sensor and to a method for its production and particularly to a temperature sensor, preferably a platinum temperature sensor, with space-saving contact terminals and a method for the production of such a temperature sensor.
2. Description of the Related Art
Platinum temperature sensors in thin-layer technology have been produced in various implementations for years.
German Patent Application DE 44445243 C2 describes a temperature sensor with a ceramic substrate, a resistance sensor embedded in the ceramic substrate and having a positive resistance temperature coefficient, two first lines connected to the resistance sensor and serving for current supply, two second lines connected to the resistance sensor, wherein the voltage drop at the resistance sensor may be detected by means of the two second lines, and a voltage divider resistor connected between the two second lines and in parallel to the resistance sensor, wherein the output signal voltage of the temperature sensor is present as partial voltage of the voltage divider resistor, and wherein two pads are further arranged on the surface of the ceramic substrate and connected to one of the two second lines and/or the voltage divider resistor.
German Patent Application DE 10232380 A1 describes a sensor with wire connection and a method for producing a sensor with wire connection, wherein the sensor comprises a first insulation layer, a second insulation layer with an opening, a plurality of metal conductive traces, and a plurality of electrodes, wherein each metal conductive trace includes a contact area and is arranged between the first and the second insulation layer, and wherein each electrode further includes a connection area arranged separate from the contact area, and wherein the electrodes are further in electrical connection with the contact areas through the openings.
German Patent Application DE 3733192 C1 describes a PTC temperature sensor and a method for the production of a PTC temperature sensor element for the PTC temperature sensor, wherein the PTC temperature sensor comprises two ceramic films and is designed such that the PTC resistive trace is hermetically encapsulated with respect to the measurement gas and the ambient air, and wherein the PTC resistive trace is further connected to the contact areas on the other side of the film through two punched vias.
With respect to FIGS. 1 and 2, a conventional method for the production of a platinum sensor according to an approach as it is known in prior art will be explained below in more detail. In FIGS. 1 and 2, the figure parts A each show top views of the temperature sensor, and the figure parts B each show side views. Such sensors are known from DE 10020932 C1.
In the conventional approach, as it is shown in FIG. 1, a sensor structure 12, preferably a meandering platinum resistive trace, is applied to a substrate 10. The resistive trace 12 has a first end 12a and a second end 12b. Furthermore, a first contact area 14 and a second contact area 16 are arranged on the substrate 10, wherein the first contact area 14 is connected to the first end 12a of resistive trace 12, and wherein the second contact area 16 is connected to the second end 12b of the resistive trace 12.
For the completion of the temperature sensor, as shown in FIG. 2, a first connecting wire 18 is affixed to the first contact area 14, and a second connecting wire 20 is affixed to the second contact area 16. Furthermore, a protective layer 22 is preferably applied over the resistive trace 12 (see FIG. 2B). The connecting wires 18, 20 are further preferably additionally fixed by means of a glaze 24 also partially covering the cover 22.
FIG. 3 also shows a conventional temperature sensor in which the temperature sensor element is of the SMD type. Unlike the embodiment described with respect to FIGS. 1 and 2, the resistive trace 12 is arranged on the substrate 10 such that the respective ends 12a and 12b of the resistive trace 12 are arranged adjacent to opposite ends of the substrate 10 at which there are also arranged the contact areas 14 and 16. Similarly to FIGS. 1 and 2, it may also be provided here to cover the resistive trace 12 with a protective layer 22 (see FIG. 3B).
The temperature sensors described with respect to FIGS. 1 to 3 have been produced in various implementations and used for precise temperature measurement tasks for years, as has been mentioned. The typical structure of these sensor elements, as described with respect to FIGS. 1 to 3, includes an Al2O3 ceramic substrate 10 on which a platinum film 12 having a thickness of about 1 μm is applied. The platinum film is further structured so that the resistive trace has a resistance in the order of, for example, 100 ohm. This platinum resistive trace 12 is usually protected by the protective layer 22 (for example a glaze layer). The connecting wires 18, 20 are generally welded to the two contact areas 14, 16, with the exception of SMD types, wherein the wires are additionally provided with the glaze drop 24 to allow mechanical stress on the connecting wires 18, 20 during further processing.
For years there has been a tendency in prior art that the thin-film sensor elements described by way of example with respect to FIGS. 1 and 2 have become smaller and smaller, having, for example, a width of 1 mm, a length of 1.5 mm and a height of 0.8 mm, or even smaller. This is accompanied by a simultaneous increase in the nominal resistance values, for example to 1,000 ohm or even higher.
In the implementations currently known, both the resistor structure and the contact zone for the application of connecting wires and/or, for SMD devices or SMD-like implementations, the contact zone and/or the contact pads are arranged on the same plane, i.e. on the substrate surface, as can be seen in FIGS. 1 to 3. With the increasing miniaturization and the simultaneously increasing requirement to generate a high nominal resistance value, ever finer structures (resistive traces) have to be created, wherein a certain area portion always has to be reserved for the two contact areas. These contact areas 14, 16 may occupy considerably more than 50% of the overall area of the surface of the substrate 10 in comparably short elements, because, for example, the wire structure on the chip may not become infinitely short for reasons of mechanical strength. This area portion is not available for the resistive structure and therefore has to be compensated for by very fine traces, i.e. small trace widths, because the thickness of the platinum film used and/or the metal film used may not be produced infinitely thin.
However, in the case of very fine trace widths, for example of less than 5 μm, the structuring becomes more and more difficult, because the planarity of the substrates or other spurious effects (e.g. very fine dust in spite of the clean room, minimal variations in the photoresist process) also have a more and more negative effect and result in less yield.